In most Protestant Bibles, There are 39 books in the Old Testament and 27 books in the New Testament. The Catholic Bible also includes the Apocrypha, which contains an additional 15 books. Then there are the Gnostic writings known as the codices, which were found in Nag Hammadi. With so many texts floating around how did they know what was supposed to be included and what wasn't? This is an important question for us to ask and investigate in our journey as believers.

There are two versions of the Old Testament—the original Hebrew which does not include the Apocrypha, and the Greek translation which does.[5] By the time of Jesus, there was an accepted canon of which Jesus frequently quotes.[1][2] Jesus also confirms the Old Testament by referencing the three divisions of the Old Testament in Luke 24:44. BiblicalTraining.org has a thorough article on the canonization of the Old Testament which can be found here. Many discoveries concerning the Old Testament stem from the archeological find of the Dead Sea Scrolls.

The New Testament is much more complicated in terms of how the cannon was determined. Jesus confirmed the books of the Old Testament by fulfilling prophecies, quoting the scripture, and not condemning the books. If there was a problem or forgery in the Old Testament, Jesus would have called the Pharisees out on this error (after all He called them out on many other misguided practices). However, we don't have that luxury for the New Testament. In addition to Matthew, Mark, Luke, and John, there are also gospels attributed to Mary Magdalene, Peter, James, Thomas, and others.[3] How did people determine which should be included and which should not? Also, how do we know they chose the right books?

Bible.org gives an overview on the canonization of the New (and Old) Testament in the article The Bible: The Holy Canon of Scripture. Most believers use the following criteria to confirm scripture as canon:[4]

Prayer and relationship with God is the only way to know for sure what is right. The best covering of this topic I've found can be found in the article entitled "How Do You Know that the Bible is Divinely Inspired."

The following table lists the books currently considered to be inspired by some (or all) denominations within Christianity.